Semiconductive materials that exhibit the Seebeck effect in the presence of a temperature gradient are useful for the production of electricity from waste heat as well as to input electricity to move heat from one side to effect cooling. The class of semiconductive materials exhibiting the Seebeck effect is hereinafter called thermoelectrics or thermoelectric materials.
A number of contemporary thermoelectrics comprise alternating p-type and n-type semiconductor elements connected by metallic connectors. Many contemporary thermoelectrics present various disadvantages, including, in some instances, high material costs, high costs of production, difficulty of manufacture, the use of rare elements, the use of potentially carcinogenic or toxic substances, and limited formability as well as operating temperature limitations and very high coefficient of thermal expansion.
The Seebeck coefficient (S) of a material is a measurement of the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material. Optimally, a highly efficient thermoelectric material should have a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity and be able to operate at high temperatures, meaning it should have a low coefficient of thermal expansion. Other considerations arise as well. It is desirable that a thermoelectric material be susceptible to being worked to construct planar and complex net-shaped objects that can be fitted into locations where they may be used to recover waste heat. Such a thermoelectric material should have a cross section with properties to maintain a sufficiently high temperature differential between the two opposing sides in order to generate voltage efficiently. It is also desirable that a thermoelectric material have high tensile strength, have resistance to thermal shock, meaning strength and low coefficient of thermal expansion, and be formable into layers to allow the creation of graded indices for electrical, thermal, or other parameters—allowing one thermoelectric material to serve as the basis for a range of thermoelectric devices.
Silicon metal is of important value in certain chemical applications as a feedstock and/or feedstock precursor in products such as glass, silicone, silanes and many other materials. In virtually all cases, the state of the silicon to be introduced includes small particle sizes, in the range of microns or nanometers, narrow particle size distribution, and a surface substantially or completely free of oxygen, water, compounds having hydroxyl groups, or other oxidative groups. Providing small particle sizes of metallic silicon particulates with surfaces substantially or completely free of oxidative groups is important to use quantum size effects associated with silicon nanostructures to reduce the thermal conductivity of the silicon by two orders of magnitude and keeping oxide free to effect very high electrical conductivity, as well as for improving the efficiency, yield, and quality, while reducing the costs of producing high quality optical glasses, silicon based computer chips, and other products utilizing silicon based materials.